Production of tertiary amine oxides

ABSTRACT

Exothermic oxidation of tertiary amine with aqueous hydrogen peroxide in an aqueous reaction medium formed or being formed from tertiary amine, aqueous hydrogen peroxide, carbon dioxide, and optionally chelating agent and/or additional water, is initiated at about 15 to about 25° C., and while agitating the reaction mixture, the temperature is allowed to rise adiabatically to a temperature in the range of about 50 to about 100° C. In this way, it is possible to produce tertiary amine oxides with very low levels, if any, of nitrosamine impurity, without addition of metal and/or phosphorus-containing components recommended in the prior art. Even though a substantial portion of the reaction is performed at temperatures in the range of about 50-100° C., nitrosamine content, if any, in the resultant tertiary amine oxide product can be well below 30 ppb, and the free amine content, if any, can be well below 0.3 wt %. Use of such relatively exothermically achieved high temperatures in turn results in faster reaction rates and enables use of shorter reaction periods.

REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of commonly-owned prior application Ser.No. 09/053,444, filed Apr. 1, 1998, now U.S. Pat. No. 6,080,889.

TECHNICAL FIELD

This invention relates to novel process technology for producingtertiary amine oxides and to novel and eminently useful tertiary amineoxide compositions which are provided by this invention. When properlycarried out, the process technology of this invention enables the directsynthesis and provision of tertiary amine oxide surfactants havingextremely low levels, if any, of nitrosoamines (commonly known asnitrosamines), as well as possessing other important characteristics,including low free amine content.

BACKGROUND

Typically, amine oxides are produced by combining a tertiary amine andhydrogen peroxide in the presence of water. The typical prior artprocess, whether or not a reaction promoter is employed, is anisothermal process wherein the amine and water, and promoter if used,are heated before addition of peroxide in order to initiate thereaction. Because the reaction is exothermic, once the reaction has beeninitiated by heat input, the reaction mixture must be cooled to controlthe temperature of the reaction. After the majority of the reaction iscompleted, additional heat must be added to the system to achieve afinal conversion.

When the typical prior art amine oxide process is carried out attemperatures above 60° C., significant amounts of nitrosamines areproduced. Nitrosamine impurities in amine oxides have long been regardedas harmful impurities by most in the surfactant industry because ofsuspected carcinogenic and mutagenic properties. See for example"Nitrosamines: Assessing the Relative Risk" in Chemical & EngineeringNews, pages 20-26, Mar. 31, 1980. Nevertheless, according to U.S. Pat.No. 5,498,791 (Mar. 12, 1996), commercial amine oxides contain between200-1000 ppb nitrosamines.

Heretofore various attempts have been made to reduce the levels ofnitrosamines in amine oxides. According to U.S. Pat. No. 5,223,644 (Jun.29, 1993): "The method generally recommended in the prior art forreducing the nitrosamine levels has been to carry out the reaction atrelatively low temperatures, e.g., below 40° C., using the carbondioxide catalyst to maintain adequate reaction rates. We have found inpractice, however, that this approach is not generally effective toproduce amine oxides with the desired low nitrosamine content,especially when excess of hydrogen peroxide is used, as has been normalpractice to avoid products contaminated with substantial residualunreacted amine." It appears that the prior art referred to in theforegoing quotation is EP 307 184 A2, published Mar. 15, 1989, whereinit is pointed out that tert-amine oxides that are substantially free ofnitrosamine impurities can be made by reacting the desired tert-amineswith aqueous hydrogen peroxide in the presence of a promoter formed fromcarbon dioxide if the reaction is conducted at a temperature of 45° C.or lower and preferably below 40° C.

In U.S. Pat. No. 5,223,644, it is proposed to inhibit nitrosamineformation in tertiary amines to levels below 100 ppb and preferablybelow 50 ppb by including in the tert-amine/hydrogen peroxide reactionmixture or in the resultant tert-amine oxide greater than about 2.5% andup to 20% by weight of the tert-amine of a bicarbonate or carbonate suchas an alkali or alkaline earth metal bicarbonate or carbonate, notablysodium bicarbonate.

U.S. Pat. Nos. 5,442,113 (Aug. 15, 1995) and 5,498,791 (Mar. 12, 1996),acknowledge that the use of such relatively high concentrations ofcarbonates and/or bicarbonates (greater than 2.5% by weight of theamine) to inhibit the formation of nitrosamines "may result in levels ofinorganic impurity in the product which are unacceptable to somecustomers." The approach taken in these two patents is to employ asynergistic mixture of alkali or alkaline earth metal bicarbonate orcarbonate such as sodium bicarbonate, with a phosphonate such as anorganoamino methylene phosphonate.

From the information presently available, it appears that no previouslyknown process for producing tertiary amine oxides on an industrial scaleproduced or had the capability of producing a product having both a verylow content of nitrosamine and a very low content of free amine. Forexample, replication of several Examples of U.S. Pat. No. 5,223,644using a commercially available mixture of dimethyldodecylamine anddimethyltetradecylamine (ADMA® amine; Albemarle Corporation) in lieu oflauryl myristyl amine produced tertiary amine oxide products that hadlow nitrosamine contents but which had substantial quantities of freeamine (almost 3 wt %). Tertiary amine oxide product produced byAlbemarle Corporation heretofore did achieve low levels of nitrosamine,but free amine levels were typically 0.5 wt %. Unfortunately, free aminehas a deleterious effect upon the stability of hypochlorite bleaches.

It would be of great advantage if a way could be found of inhibitingformation of nitrosamines during production of tert-amine oxides by theoxidation of tert-amine with hydrogen peroxide without need for additionof metal or phosphorus compounds and consequent contamination of theproduct with such impurities, especially if the reaction could be safelycarried out using temperatures above 40-45° C. It would also be of greatadvantage if it were possible to provide a tertiary amine oxide productthat has very low contents of both nitrosamine and free amine. Thisinvention is deemed to fulfill these needs in a highly effective manner.

THE INVENTION

It has been discovered, inter alia, that it is possible to producetertiary amine oxides with very low levels, if any, of nitrosamineimpurity and very low levels, if any, of free amine impurity, byoxidation of tertiary amine with aqueous hydrogen peroxide withoutaddition of metal and/or phosphorus-containing components. Moreover, ithas been found possible to conduct a substantial portion of the reactionat temperatures in the range of about 50 to about 100° C. while at thesame time maintaining very low levels of nitrosamine and free aminecontents, if any, in the resultant tertiary amine product. Use of suchrelatively high temperatures in turn results in faster reaction ratesand enables use of shorter reaction periods. And as a consequence ofthis invention, it is also now possible to provide highly pure tertiaryamine oxide products which have very low levels, if any, of nitrosamineand free amine impurities, and very low levels of metal impurities, andbecause no phosphorus additives are needed in the process, the tertiaryamine oxide products of this invention are devoid of phosphorusresulting from use of phosphorus additive. Since it is preferred not toemploy organic solvents or diluents in the aqueous reaction medium, thisinvention also makes it possible to provide tertiary amine oxideproducts that are devoid of organic impurities resulting from use oforganic solvent or diluent in the process. Moreover, all of theseadvantages can be achieved in operations readily, efficiently, andsafely conducted on an industrial plant scale.

Thus, in accordance with one of the embodiments of this invention, thereis provided a process for producing tertiary amine oxide which comprisesoxidizing tertiary amine with hydrogen peroxide in an aqueous reactionmedium, the aqueous reaction medium having been formed or being formedfrom tertiary amine, aqueous hydrogen peroxide, carbon dioxide, andoptionally chelating agent and/or additional water, the exothermicoxidation reaction being initiated at a temperature in the range ofabout 15 to about 25° C., and while agitating the reaction mixture,allowing the temperature of the reaction mixture to rise adiabaticallyto a temperature in the range of about 50 to about 100° C., such thattertiary amine oxide is produced. Preferably, the reaction is conductedin a thermally insulated reactor. Products having 30 ppb or less, ifany, of nitrosamine impurity and 0.3 wt % or less, typically 0.2 wt % orless, if any, of free amine can be produced by proper conduct of theprocess of this invention.

Without being bound by theory, it is believed that a tenable explanationfor the surprisingly low levels, if any, of nitrosamine impurity in theproduct results from substantially uniform temperatures andsubstantially uniform rate of temperature increase being developedthroughout the entire reaction mixture as a result of the exothermicreaction taking place throughout the entire suitably-agitated reactionmixture. In other words, significant differences in temperature withinthe reaction mixture at each given increment of time, such as localizedhigher temperature regions in the reaction mixture close to the reactorwalls as compared to the temperature of interior portions of thereaction mixture at any given instant of time, are minimized by suitableagitation and avoidance of external heat input through the reactorwalls. Likewise, heat input to the reaction mixture via internal heatingcoils resulting in cooler regions of reaction mixture close to reactorwalls and rapid flow of heat through the reactor walls are avoided.Thus, once the reaction has been initiated, the temperature of thereaction mixture continuously rises due to the exothermic nature of thereaction, yet at each given instant of time the temperature is deemedsubstantially uniform throughout the entire reaction mixture. Whethersuch uniform temperature conditions also play a role in the formation ofproduct having low free amine contents is not known, but the possibilityexists.

It will be seen, therefore, that the above embodiment of this inventiontakes full advantage of the exotherm produced by the oxidation oftertiary amine to tertiary amine oxide by hydrogen peroxide. In thisway, the need to supply heat energy to the reaction is eliminated andthe amount of energy consumed in the process is minimized. In contrast,U.S. Pat. Nos. 5,442,113 and 5,498,791 (supra) regard the exotherm as aproblem to be avoided.

Again, without being bound by theory, in addition to theabove-referred-to temperature uniformity in the reaction mixture, otherfactors are believed to also contribute to the excellent resultsachievable by use of the process technology of this invention. Uniformreaction temperatures within the system above 40° C. utilizing carbondioxide as catalyst and utilizing excess hydrogen peroxide produce amineoxide with low residual free amine and with low nitrosamine levels.Because the catalyst, carbon dioxide, acts as a neutralizing agent tothe amine, the basicity of the solution is reduced, thus stabilizing theperoxide in the reaction solution. The stabilizing effects of the carbondioxide in turn allow the reaction to be carried out at highertemperatures without excessive peroxide decomposition. Moreover, becausethe catalyst acts as a neutralizing agent, the amine, water, andperoxide solution are able to form an emulsion which leads to faster andmore uniform reaction initiation and progression.

Although less preferable, another embodiment of this invention simulatesto the extent reasonably feasible technically and economically, theconditions that exist during the adiabatic process of this invention. Inthis additional embodiment there is provided a process for producingtertiary amine oxide which comprises oxidizing tertiary amine withhydrogen peroxide in an aqueous reaction medium, the aqueous reactionmedium having been formed or being formed from tertiary amine, aqueoushydrogen peroxide, carbon dioxide, and optionally chelating agent and/oradditional water, the exothermic oxidation reaction being initiated at atemperature in the range of about 1 to about 25° C., and while agitatingthe reaction mixture, applying a controlled limited amount of heatenergy to the reaction mixture and maintaining a substantially uniformtemperature throughout the agitated reaction mixture whereby at anygiven moment in time the temperature differential within the reactionmixture is no greater than 5° C., and preferably no greater than 2° C.,such that the temperature of the reaction mixture is increased, andpreferably is progressively increased, to a maximum temperature in therange of about 50 to about 100° C., such that tertiary amine oxide isproduced, the major amount (i.e., more than 50%) of the heat energycausing the increase in temperature of the reaction mixture beingderived from the exothermic reaction itself, with the balance of thethermal energy causing such temperature increase (i e., less than 50%)being supplied by the application of said controlled limited amount ofthermal energy to the reaction mixture. By proper selection andcoordination of the reaction initiation temperature, the volume of waterin the reaction mixture, the amount of heat energy supplied to thereaction mixture, and the rate of agitation of the reaction mixture, itis possible to produce tertiary amine oxides having very low levels ofnitrosamine and free amine content without need for use of specialadditives such as metal carbonates or bicarbonates, and/or phosphorusadditives of the prior art.

Still another embodiment of this invention provides an aqueous solutionof tertiary amine oxide wherein the content of tertiary amine oxide isin the range of about 25 to about 35 wt %; wherein the content ofnitrosamine, if any, is 30 ppb (wt/wt) or less; and wherein the contentof amine, if any, is 0.3 wt % or less. Preferably, but not necessarily,the total content of alkali metal (e.g., Na), if any, is 10 ppm (wt/wt)or less; and the total content of alkaline earth metal, if any, (e.g.,Mg and Ca) is 1 ppm (wt/wt) or less; each foregoing wt %, ppb, and ppmbeing based on the weight of the solution. So far as is known, it hasnever been possible heretofore to prepare a tertiary amine oxidesolution having the foregoing attributes and characteristics by use ofany previously described process, muchless one involving the oxidationof a tertiary amine by aqueous hydrogen peroxide. In this connection, asused anywhere in the specification or claims hereof "ppb" means partsper billion parts, a billion being 10⁹ or a thousand million; "ppm"means parts per million parts, a million being 10⁶ ; and as indicated by"wt/wt" the parts are parts by weight. In addition to the foregoingattributes and characteristics, the solutions of this inventionpreferably have a content, if any, of no more than about 1 wt % hydrogenperoxide, and more preferably no more than about 0.5 wt % hydrogenperoxide, based on the weight of the solution. Also preferred aresolutions wherein the content of titanium, if any, is 0.1 ppm (wt/wt) orless; wherein the content of iron, if any, is 1.0 ppm (wt/wt) or less;wherein the content of cobalt, if any, is 0.3 ppm (wt/wt) or less;wherein the content of nickel, if any, is 0.5 ppm (wt/wt) or less; andwherein the content of copper, if any, is 2 ppm (wt/wt) or less, andmost preferably 0.5 ppm or less.

Preferred solutions are those in which the tertiary amine oxide is oneor more compounds of the formula

    R.sup.1 R.sup.2 R.sup.3 N=0

where R¹ is a methyl or ethyl group, R² is a primary alkyl group havingin the range of about 8 to about 20 carbon atoms, and R³ is,independently, a methyl group, an ethyl group, or a primary alkyl grouphaving in the range of about 8 to about 20 carbon atoms. Compounds ofthis formula wherein R¹ and R³ are methyl groups and R² is a straightchain primary alkyl group are particularly preferred. Among the distinctadvantages of these solutions is that they pose no known potentialhealth hazard in use, they are extremely friendly to the environment,they leave essentially no residues during use, and they can be used informulating a wide variety of surfactant compositions that possess goodlime dispersant properties and very low destabilizing properties towardbleaches such as sodium hypochlorite.

The above and other embodiments and features of this invention will bestill further apparent from the ensuing description and appended claims.

Tertiary Amine

The amines that may be used in the process of our invention aretypically linear amines of the general formula R¹ R² R³ N, whereinR¹,R², and R³ represent straight or branched chain alkyl groups, alkenylgroups or aralkyl groups which may be the same or different. They may belower alkyl groups, i.e., of from 1 to 7, preferably 1 to 4, carbonatoms, but in a preferred embodiment of this invention, the tertiaryamines may instead be represented by the general formula (R)_(m) R¹)_(n)N, wherein m=1 or 2 and n=(3-m). In this latter formula, the groupsdesignated R, which may be the same or different, represent C₈ -C₂₄alkyl or alkenyl polyalkyleneoxy groups, C₇ -C₂₃ esteralkyl oresteralkenyl groups, amidoalkyl or amidoalkenyl groups, and the R¹groups, which may also be the same or different, represent C₁ -C₄ alkyl,alkoxy or hydroxyalkyl, or polyalkyleneoxy groups. The polyalkyleneoxygroups are preferably polyethyleneoxy groups or polypropyleneoxy ormixed ethyleneoxy and propyleneoxy groups containing between 1 and 20ethyleneoxy and/or propyleneoxy groups. The amidoalkyl groups arepreferably C₇ -C₂₃ alkylamidopropyl groups or alkenylamidopropyl groups.

Alternatively, the amines may comprise cyclic amines such asimidazolines or pyridines, N-substituted piperazines, or N-substitutedmorpholines, e.g., N-methyl morpholine.

Preferred tertiary amines used in the process of this invention are oneor more compounds of the formula R¹ R² R³ N where R¹ is a methyl orethyl group, R² is a primary alkyl group having in the range of about 8to about 20 carbon atoms, and R³ is, independently, a methyl group, anethyl group, or a primary alkyl group having in the range of about 8 toabout 20 carbon atoms. Compounds of this formula wherein R¹ and R³ aremethyl groups and R² is a straight chain primary alkyl group areparticularly preferred. Dimethyl decyl amine, dimethyl dodecyl amine anddimethyl tetradecyl amine are especially preferred reactants for use inpreparing aqueous surfactant solutions pursuant to this invention.

Hydrogen Peroxide

As noted above, the hydrogen peroxide is typically employed as a watersolution of any suitable concentration. Preferably the hydrogen peroxideis employed as a 30 to 70 wt % aqueous solution. Particularly preferredsolutions are 30 to 40 wt % aqueous hydrogen peroxide solutions. Theamount of hydrogen peroxide employed in the reaction should be at leasta stoichiometric amount (i.e., at least 1 mole of hydrogen peroxide permole of tertiary amine). Preferably, an excess amount of hydrogenperoxide is used, and in this case an excess in the range of about 1.01to about 1.2 moles of hydrogen peroxide per mole of tertiary amine ispreferred. It is especially preferred to employ these reactants in amole ratio of about 1.01 to about 1.05 mole of hydrogen peroxide permole of tertiary amine. These latter ranges when utilized in thepractice of this invention make it possible to form a finished producthaving an extremely low content of both free amine and hydrogen peroxideimpurities.

Chelating Agent

An optional, but preferable, component used in the reaction mixtures isat least one suitable chelating agent such as ethylenediaminetetraacetic acid or a water-soluble salt thereof, diethylenetriaminepentaacetic acid or a water-soluble salt thereof, or S,S-ethylenediaminedisuccinic acid or a water-soluble salt thereof. Other suitablechelating agents include nitrilotriacetic acid or a water-soluble saltthereof. The chelating agent, which serves as a sequestrant for metalions which may be derived by extraction from metallic reactor walls,piping or the like, is preferably a metal-free chelating agent. In thisway the chelating agent as added to the reaction mixture does not itselfintroduce any metal constituent(s). Thus, if used as a salt, it ispreferably an ammonium salt, although because of the small amounts ofchelating agent used, alkali metal salts such as the sodium salts areacceptable for use. Typically, the amount of chelating agent used willfall in the range of about 0.01 to about 0.1 wt %, and preferably in therange of about 0.05 to about 0.1 wt %, based on the total weight of thereaction mixture.

Of the chelating agents suitable for use, ethylenediamine tetraaceticacid, diethylenetriamine pentaacetic acid, and S,S-ethylenediaminedisuccinic acid are the three most preferred materials.

Water

For best results the water used should be free of appreciable quantitiesof dissolved metals. While it is not necessary to employ deionized ordistilled water, such materials can be used if desired. Ordinary tapwater is satisfactory provided that it has a metallic content, if any,of not more than 5 ppm. Ordinarily, at least a portion of the wateremployed in producing the reaction medium will be provided by theaqueous hydrogen peroxide solution. However, oftentimes it is desirableto increase the amount of water over and above that provided by theaqueous hydrogen peroxide being used in making up the reaction mixture.In general, the amount of water should correspond in quantity to thequantity desired in the finished amine oxide solution to be produced inthe process, as this eliminates the need for subsequent operations suchas further dilution with water, or distillation of excessive quantitiesof water from the aqueous product solution produced in the reaction.Thus, if a 30 wt % solution of amine oxide is the target product, thetotal amount of water introduced into the reaction mixture shouldcorrespond to approximately 70 wt % of the projected total weight of theamine oxide solution being formed.

Carbon Dioxide

An essential ingredient charged to the reaction mixture is carbondioxide. Although it may be charged in the form of so-called dry ice, itis preferable to introduce the carbon dioxide in gaseous form and tointroduce the same at a locus below the surface of the liquid reactionmixture. The carbon dioxide serves as a reaction catalyst or reactionpromoter. In this connection, the precise chemical make-up of the carbondioxide-derived catalyst is not known with certainty. It may be that thecarbon dioxide itself catalyzes or promotes the reaction. However, it isequally possible that the carbon dioxide reacts in situ to form eithercarbonic acid or some unidentified complex or other substance whichserves as the actual catalytic entity. It will thus be understood thatthis invention is not limited to the particular form or chemicalcomposition of the reaction catalyst or reaction promoter resulting fromthe introduction into the reaction mixture of carbon dioxide as aningredient.

Typically, the amount of carbon dioxide introduced into the aqueousreaction mixture should be such as to result in the reaction mixtureinitially achieving a pH in the range of about 7 to about 8, andpreferably in the range of about 7.3 to about 7.8.

Modes of Addition

The various ingredients making up the reaction mixture can be introducedinto the reactor in a number of sequences. For example, each of theingredients (tertiary amine, aqueous hydrogen peroxide, carbon dioxide,additional water if used, and chelating agent if used) can be introducedindividually or in any suitable subcombinations and in any suitableorder into the reactor in the total quantities to be used with nofurther feed of any ingredient during the course of the reaction. Whenconducting the reaction in this manner (i.e., with all of theingredients charged at the outset), the only preference is that eitherthe carbon dioxide or the aqueous hydrogen peroxide should be the lastingredient introduced into the reaction mixture, as the reaction will beinitiated upon the introduction of either such ingredient to the mixturecomprising the other such ingredient and the tertiary amine. Thus, inone such embodiment the aqueous reaction medium is formed by mixingtogether tertiary amine, carbon dioxide, optionally chelating agent, andoptionally water, and then introducing aqueous hydrogen peroxide intothe reaction mixture to initiate the exothermic reaction. In anothersuch embodiment the aqueous reaction medium is formed by mixing togethertertiary amine, aqueous hydrogen peroxide, and optionally chelatingagent and/or additional water, and then introducing carbon dioxide toinitiate the exothermic reaction. Still another such embodiment involvesforming the reaction mixture by introducing tertiary amine, andoptionally chelating agent and/or water, into a reactor, and thenintroducing concurrently or in any sequence, aqueous hydrogen peroxideand carbon dioxide to initiate the exothermic reaction. In theory thetertiary amine could be the last ingredient charged to the reactionmixture, however, this is less desirable as it could result in excessivepremature oxidation of the tertiary amine with adverse consequences.

Instead of charging all of the reactants at the outset it is possible,and in some cases preferable, to introduce one or more of theingredients to the reaction mixture portion wise, and continuouslyand/or intermittently, as the reaction proceeds. In this mode ofaddition there are various preferred embodiments. In one such embodimentthe aqueous hydrogen peroxide is introduced portion wise, continuouslyand/or intermittently, into the reaction mixture initially composed oftertiary amine, carbon dioxide, chelating agent if used, and water ifused. Some of the hydrogen peroxide can also be present in the initialreaction mixture. In another such embodiment aqueous hydrogen peroxideand carbon dioxide are concurrently introduced portion wise,continuously and/or intermittently, into the reaction mixture initiallycomposed of tertiary amine, chelating agent if used, and water if used.Here again a portion of the carbon dioxide and/or hydrogen peroxide canbe present in the initial reaction mixture. Still another variant is tointroduce carbon dioxide portion wise, continuously and/orintermittently, into the reaction mixture initially composed of tertiaryamine, aqueous hydrogen peroxide, chelating agent if used, andadditional water if used. Once again the initial reaction mixture mayalso contain a portion of the carbon dioxide.

Accordingly, this invention contemplates the addition of the respectiveingredients into the reaction mixture being formed in any suitablemanner (individually and/or in any suitable subcombination(s),concurrently and/or in any suitable sequence.

Thermal Insulation

Preferably the reactor used in the practice of the process of thisinvention is provided with thermal insulation of any suitable type. Theuse of thermal insulation having a suitably high R value reduces theextent to which thermal energy can pass into or out of the reactionvessel and thus into or out of the reaction mixture undergoing anadiabatic reaction. In the embodiment of this invention wherein anadiabatic reaction is simulated, a jacketed reactor can be employed inwhich a controlled amount of heat energy is supplied to the reactionmixture by means of the heated fluid flowing through the jacket of thereactor. Preferably, as the temperature of the reaction mixture rises byvirtue of the exothermic reaction, the temperature of the water fed toand flowing through the jacket is correspondingly elevated so that theamount of heat loss or gain through the reactor walls is minimized.

While it is preferred to employ a thermally insulated reactor whenconducting the process of this invention, this is not required. Theprocess of this invention can be carried out effectively in conventionalreactors devoid of any special thermal insulation, especially when thereaction mixture is suitably agitated to ensure substantially uniformcomposition throughout the reaction mixture undergoing adiabaticreaction.

Agitation

In order to ensure that at any given moment of time the temperaturewithin the entire reaction mixture is substantially the same, it isimportant to suitably agitate the reaction mixture to form asubstantially uniform emulsion or emulsion-like reaction mixture. Inthis way, the reaction tends to take place substantially uniformly atall locations within the reaction mixture, which in turn results in aprogressive increase in the substantially uniform temperature of thereaction mixture. Thus, it is desirable to employ a reactor equippedwith suitable mechanical stirring apparatus. However, other forms ofagitation such as use of a rocking autoclave are also feasible.

Temperature and Pressure Conditions

In the embodiments wherein the process of this invention is conductedcompletely adiabatically, the exothermic oxidation reaction is initiatedat a temperature in the range of about 15 to about 25° C., and whileagitating the reaction mixture, allowing the temperature of the reactionmixture to rise adiabatically to a temperature in the range of about 50to about 100° C., and preferably in the range of about 60 to about 80°C. such that tertiary amine oxide is produced. In the embodiments wherea major amount (i.e., more than 50%) of the heat energy causing theincrease in temperature of the reaction mixture is derived from theexothermic reaction, with the balance of the thermal energy causing suchtemperature increase (i.e., less than 50%) being supplied by theapplication of a controlled limited amount of thermal energy, thereaction is initiated at a temperature in the range of about 1 to about25° C., and while agitating the reaction mixture and keeping thetemperature substantially uniform throughout the entire mixture at eachmoment in time, a controlled limited amount of heat energy is applied tothe reaction mixture to a maximum temperature in the range of about 50to about 100° C., such that tertiary amine oxide is produced. In allsuch embodiments the reaction can be conducted in an open system atambient atmospheric pressure, or it can be conducted in a closed systemunder superatmospheric pressure such as autogenous pressure orexternally applied pressure.

Analytical Procedures

Any suitable procedure can be used for determining content variousimpurities in the reaction mixtures produced in the process. Forconvenience, the following procedures (or other procedures of at leastequivalent accuracy) are recommended:

To determine free amine in the aqueous solution of tertiary amine oxide,a sample of amine oxide is reacted with acetic anhydride in the presenceof acetic acid under reflux conditions. The sample is cooled andtitrated potentiometrically with 0.1 N HClO₄ in acetic acid.

To determine alkali metal or alkaline earth metal content in the aqueoussolution of the tertiary amine oxide, a sample of aqueous amine oxide isdigested with sulfuric acid at 380° C. Nitric acid is added as needed tokeep the solution clear. The mixture is charred until only 1 mL remainsin the beaker. Deionized-distilled water and concentrated nitric acidare added to form a solution. The mixture is allowed to again cool. Theresulting solution is analyzed by inductively coupled plasma (ICP)emission spectroscope using a Perkin-Elmer Optima 3000, or equivalentdevice.

To determine titanium, iron, cobalt, nickel, and copper content in theaqueous solution of the tertiary amine oxide, a sample of aqueous amineoxide is digested with sulfuric acid at 380° C. Nitric acid is added asneeded to keep the solution clear. The mixture is charred until only 1mL remains in the beaker. Deionized-distilled water and concentratednitric acid are added to form a solution, and the mixture is allowed toagain cool. The resulting solution is analyzed by inductively coupledplasma (ICP) emission spectroscopy. For this analysis, a Perkin-ElmerOptima 3000, or equivalent device is employed.

To determine hydrogen peroxide in the aqueous solution of the tertiaryamine oxide, a dilute sample of aqueous amine oxide is reacted withpotassium iodide and titrated with sodium thiosulfate. A quantitativeamount of iodine is formed from the available peroxide in a givensample.

Total N-nitrosamine content (TNC) is determined by a chemilurninescencemethod in which nitrite ions in the sample are destroyed by sulfuricacid, the sample is denitrosated using HBr/acetic acid, and the nitricoxide (NO) liberated from the sample is fed into a chemiluminescenceanalyzer. The nitric oxide reacts with ozone in the analyzer to produceexcited NO₂. As the NO₂ decays to the ground state, light is emitted inthe near infrared region, and this signal can be integratedelectronically. It has been reported that the limit of detection by thismethod is 10 ppb reported as the --NNO species (mw=44).

The following examples are illustrative of ways by which the process ofthis invention can be carried out. These examples are not intended tolimit, and should not be construed as limiting, the invention to theparticular procedures described.

Example 1

The following general procedure for the conduct of an adiabatic processtypically produces amine oxides containing <30 ppb total nitrosamines.Dimethyl decyl amine (ADMA®-10 amine; Albemarle Corporation) (200.3 g,1.08 mol), 35% aqueous hydrogen peroxide (108.1 g, 1.11 mol, 4% molarexcess), 409.8 mL of water, and diethylene triamine pentaacetic acid(DTPA) (0.5 g, 1.3 mmol), are added to an thermally insulated roundbottom flask. The insulation is a mantle of fiberglass wool. Carbondioxide is introduced to the reactor in 1.6 wt % relative the chargedamine. Introduction of a sufficient amount of CO₂ catalyst is indicatedby reduction in the pH of the amine/water mixture to a pH of 7.5-7.8.Continuous supply of catalyst is not necessary if enough is introducedinitially. The reaction quickly initiates and is allowed to continueadiabatically to the maximum temperature caused by the exotherm. Themaximum temperature in reactions carried out in this manner and scale istypically 75-80° C., and is typically achieved in about 20 to 30 minutesafter introduction of the CO₂ catalyst. The temperature remains high andno cooling is applied until the reaction mass contains <0.3 wt %residual free amine. The reaction is typically completed within 2 hoursof catalyst introduction. Over the two-hour period, the temperaturedecreases to about 62° C. In a reaction carried out in this manner, thetotal nitrosamine content in the aqueous product solution of dimethyldecyl amine oxide, as measured by chemiluminescence, was 11 ppb (wt/wt).

Example 2

A procedure similar to that of Example 1, but in which the hydrogenperoxide is metered into the reaction mixture over time produces likeresults. Thus, dimethyl decyl amine (ADMA®-10 amine; AlbemarleCorporation) (201.8 g, 1.09 mol), 410.0 mL of water, and diethylenetriamine pentaacetic acid (DTPA) (0.5 g, 1.3 mmol), are added to athermally insulated round bottom flask. The flask is insulated withglass wool. The organic/water mixture is treated with carbon dioxideprior to charging the hydrogen peroxide. The 35% aqueous hydrogenperoxide (108.6 g, 1.12 mol, 4% molar excess) is charged over a periodof 35 minutes along with additional carbon dioxide. During that periodthe temperature rises 54° C. The maximum temperature achieved was 74° C.During the 90-minute cook, the temperature decreased by 11° C. Two hoursafter the peroxide addition began, the free amine was measured to be0.21 wt % (99.2% conversion) and the residual hydrogen peroxide was 0.25wt %. The level of nitrosamine was 10 ppb (wt/wt).

Example 3

Combined in a round bottom flask at ambient temperature (ca. 20° C.)were 191.2 grams (0.90 mol) of dimethyl dodecyl amine (ADMA®-12 amine,Albemarle Corporation), 393.3 grams of tap water (essentially zerohardness), and 0.5 gram of DTPA. The flask was insulated with a mantleof glass wool. Catalyst was then introduced to the flask through asubsurface dipleg prior to hydrogen peroxide addition. 84.0 (0.94 mol)Grams of 35% hydrogen peroxide (4% excess) was fed over a 40-minuteperiod. The reaction was allowed to proceed adiabatically until thetemperature of the reaction mass reached a maximum temperature of 68° C.At this point the reaction mass began to cool because the reaction wasessentially completed. Within 3 hours of introduction of catalyst andhydrogen peroxide, the reaction was completed. The total nitrosaminecontent of the sample was 8 ppb.

Example 4

In this procedure carbon dioxide catalyst was introduced slowly overtime to a system containing amine, water, peroxide and chelating agent.The rate of reaction or rate of heat generation can be controlled simplyby control of catalyst feed rate, which in turn can be controlled withreference to the pH of the system. Thus, combined in an insulated roundbottom flask at ambient temperature were 452 g ADMA®-10 amine (2.44mol), 922 mL tap water, 1.13 g DTPA (2.9 mmol), and 244.5 g 35% hydrogenperoxide. The pH of the reaction mixture was maintained at 8 by portionwise addition of carbon dioxide to the reaction mixture. A total of 3.8g carbon dioxide was added. Maximum temperature (77° C.) was achieved in35 minutes.

It can be seen that among the improvements made possible by thisinvention are the following:

1) Faster reaction and shorter reaction period,

2) Lower nitrosoamine values despite in situ generation of highertemperatures,

3) Very low metal content such as sodium in the amine oxide product, and

4) Very low residual free amine in the amine oxide product.

For comparative purposes Examples 1, 4 and 5 of U.S. Pat. No. 5,223,644were replicated using a mixture of dimethyldodecylamine anddimethyltetradecylamine (ADMA®-1214; Albemarle Corporation) as thetertiary amine. The results of these comparative runs are summarized inTable 1.

                  TABLE 1                                                         ______________________________________                                        Replicate of Replicate of  Replicate of                                         Example 1 of Example 4 of Example 5 of                                        U.S. Pat. No. U.S. Pat. No. U.S. Pat. No.                                     5,223,644 5,223,644 5,223,644                                               ______________________________________                                        31 ppb nitrosamine                                                                         33 ppb nitrosamine                                                                          25 ppb nitrosamine                                   2.95 wt % free amine 2.91 wt % free amine 2.95 wt % free amine                0.42% residual 0.03% residual 0.02% residual                                  peroxide peroxide peroxide                                                  ______________________________________                                    

In order to still further appreciate the improvements made possible bythe practice of this invention, there are summarized in Table 2 theresults of analyses of approximately 30 wt % aqueous tertiary amineoxide products available from various commercial sources. These productswere as follows:

BARLOX 12 amine oxide (Lonza Inc.) (Specification: 29.6 wt % lauryldimethyl tertiary amine oxide);

BARLOX 14 amine oxide (Lonza Inc.) (Specification: 31.4 wt % myristyldimethyl tertiary amine oxide);

AMMONYX LO amine oxide (Stephan Co.) (Specification: 30.6 wt % lauryldimethyl tertiary amine oxide);

AMMONYX MO amine oxide (Specification: 30.1 wt % myristyl dimethyltertiary amine oxide); and

EMCOL LO amine oxide (Witco Corp.) (Specification: 30.1 wt % lauryldimethyl tertiary amine oxide).

                  TABLE 2                                                         ______________________________________                                                                                 H.sub.2 O.sub.2,                       Amine Oxide Na, ppm Fe, ppm Ni, ppm Amine, wt % wt %                        ______________________________________                                        BARLOX 12 520      2.54    <0.4  0.53    0.07                                   BARLOX 14 407 2.59 <0.4 0.56 0.09                                             AMMONYX LO 358 <0.5 <0.4 0.45 0.04                                            AMMONYX MO 120 2.67 <0.4 0.22 0.00                                            EMCOL LO 564 0.11 <0.3 1.82 0.09                                            ______________________________________                                    

In the specification and claims hereof, nitrosamine content of thetertiary amine oxide product compositions of this invention refers tothe total nitrosamine content of the product, reported as--NNO species.Such species has a molecular weight of 44. Thus the nitrosamine content,if any of the tertiary amine oxide product compositions of thisinvention is independent of the organic groups to which the --NNOspecies is attached.

It is to be understood that the reactants and components referred to bychemical name or formula anywhere in the specification or claims hereof,whether referred to in the singular or plural, are identified as theyexist prior to coming into contact with another substance referred to bychemical name or chemical type (e.g., another reactant, a solvent, or,etc.). It matters not what preliminary chemical changes, transformationsand/or reactions, if any, take place in the resulting mixture orsolution or reaction medium as such changes, transformations and/orreactions are the natural result of bringing the specified reactantsand/or components together under the conditions called for pursuant tothis disclosure. Thus, the reactants and components are identified asingredients to be brought together in connection with performing adesired chemical reaction or in forming a mixture to be used inconducting a desired reaction. Accordingly, even though the claimshereinafter may refer to substances, components and/or ingredients inthe present tense ("comprises," "is," etc.), the reference is to thesubstance, component or ingredient as it existed at the time just beforeit was first contacted, blended or mixed with one or more othersubstances, components and/or ingredients in accordance with the presentdisclosure. The fact that the substance, component or ingredient mayhave lost its original identity through a chemical reaction ortransformation during the course of such contacting, blending or mixingoperations is thus wholly immaterial for an accurate understanding andappreciation of this disclosure and the claims thereof.

Likewise, the process of this invention produces "tertiary amine oxide"in an aqueous medium. By this is meant that if the water is removed, onewill recover tertiary amine oxide as a chemical product. While the"tertiary amine oxide" is in solution it may possibly be solvated,hydrated, complexed, or otherwise altered in chemical makeup, and ifsuch actually happens, the claims hereinafter are intended to cover anysuch natural consequence of carrying out the process of this inventionin the proper manner as described herein. Thus, it matters not if anysuch solvation, hydration, or other alteration in chemical makeup of the"tertiary amine oxide" occurs while in the aqueous medium as long as theprocess is being carried out properly as described and claimed herein.In short, the product of the process is identified as chemists identifyproducts, and not as lawyers or others might seek to identify them.

Each and every patent or other publication referred to in any portion ofthis specification is incorporated in toto into this disclosure byreference, as if fully set forth herein.

This invention is susceptible to considerable variation in its practice.Therefore, the foregoing description is not intended to limit, andshould not be construed as limiting, the invention to the particularexemplifications presented hereinabove. Rather, what is intended to becovered is as set forth in the ensuing claims and the equivalentsthereof permitted as a matter of law.

That which is claimed is:
 1. An aqueous solution of tertiary amine oxideconsisting essentially of water; a total content of tertiary amine oxidein the range of about 25 to about 35 wt %; a total content ofnitrosamine, if any, of 30 ppb (wt/wt) or less as determined by use ofan analytical procedure in which the limit of detection is 10 ppbreported as the --NNO species; and a total content of amine, if any, of0.3 wt % or less; each foregoing wt % and ppb being based on the weightof the solution.
 2. A solution according to claim 1 wherein the content,if any, of amine is 0.2 wt % or less.
 3. A solution according to claim 1wherein the tertiary amine oxide is one or more compounds of the formula

    R.sup.1 R.sup.2 R.sup.3 N=0

where R¹ is a methyl or ethyl group, R² is an alkyl group having in therange of about 8 to about 20 carbon atoms, and R³ is, independently, amethyl group, an ethyl group, or a primary alkyl group having in therange of about 8 to about 20 carbon atoms.
 4. A solution according toclaim 3 wherein R¹ and R³ are methyl groups and R² is a straight chainprimary alkyl group.
 5. A solution according to claim 4 wherein R² isoctyl.
 6. A solution according to claim 4 wherein R² is decyl.
 7. Asolution according to claim 4 wherein R² is dodecyl.
 8. A solutionaccording to claim 4 wherein R² is tetradecyl.
 9. A solution accordingto claim 4 wherein R² is hexadecyl.
 10. A solution according to claim 4wherein R² is octadecyl.
 11. A solution according to claim 4 wherein R²is eicosyl.
 12. An aqueous solution of tertiary amine oxide consistingessentially of water; a total content of tertiary amine oxide in therange of about 25 to about 35 wt %; a total content of nitrosamine, ifany, of 30 ppb (wt/wt) or less as determined by use of an analyticalprocedure in which the limit of detection is 10 ppb reported as the--NNO species; a total content of amine, if any, of 0.2 wt % or less; atotal content of alkali metal, if any, of 10 ppm (wt/wt) or less; and atotal content of alkaline earth metal, if any, of 1 ppm (wt/wt) or less;each foregoing wt %, ppb and ppm being based on the weight of thesolution.
 13. A solution according to claim 12 wherein the content ofhydrogen peroxide, if any, in said solution is no more than about 1 wt %based on the weight of the solution.
 14. A solution according to claim12 wherein the content of hydrogen peroxide, if any, in said solution isno more than about 0.5 wt % based on the weight of the solution.
 15. Asolution according to claim 12 wherein the content of titanium, if any,in said solution is 0.1 ppm (wt/wt) or less; wherein the content ofiron, if any, in said solution is 1.0 ppm (wt/wt) or less; wherein thecontent of cobalt, if any, in said solution is 0.3 ppm (wt/wt) or less;wherein the content of nickel, if any, in said solution is 0.5 ppm(wt/wt) or less; and wherein the content of copper, if any, in saidsolution is 0.5 ppm or less.
 16. A solution according to claim 12wherein the tertiary amine oxide is one or more compounds of the formula

    R.sup.1 R.sup.2 R.sup.3 N=0

where R¹ is a methyl or ethyl group, R² is an alkyl group having in therange of about 8 to about 20 carbon atoms, and R³ is, independently, amethyl group, an ethyl group, or a primary alkyl group having in therange of about 8 to about 20 carbon atoms.
 17. A solution according toclaim 16 wherein R¹ and R³ are methyl groups and R² is a straight chainprimary alkyl group.
 18. A solution according to claim 17 wherein R² istetradecyl.
 19. A solution according to claim 17 wherein the content ofhydrogen peroxide, if any, in said solution is no more than about 1 wt %based on the weight of the solution.